The present invention relates generally to textile fabrics and, more particularly, to textile fabrics incorporating electrically conductive yarns so as to be capable of conducting electrical current sufficiently for dissipating electrical charges.
The tendency of electrostatic charges to be generated by frictional contact with textile fabrics is well known. In particular, it is common for wearing apparel to become charged with static electricity from frictional contact with a wearer's skin or with other fabrics or garments resulting from normal body movements of the wearer. Static electricity also tends to accumulate on clothing as a result of walking on carpets and other non-conductive floor coverings.
The accumulation of such electrostatic charges normally is little more than an annoyance, causing clothing items to cling to one another or to the wearer's body and to periodically deliver minor shocks to the person when touching a grounded object or surface. In some environments, however, the accumulation of static electricity on clothing can pose a significant danger. For example, for persons working with or near flammable or explosive materials, the arcing or sparking which results from the discharge of static electricity from a person to a grounded object can potentially ignite or combust such materials. Likewise, in environments wherein microelectronic equipment such as miniaturized circuit boards or like electrically sensitive components are being manufactured or assembled, the discharge of static electricity can potentially damage the equipment.
Accordingly, considerable effort has been undertaken within the textile industry over recent decades toward the object of developing textile fabrics which resist the accumulation of static electrical charges and/or have improved capabilities of continually dissipating such charges so as to alleviate the above-discussed dangers and annoyances. Toward this end, various forms of electrically conductive yarns and various constructions of textile fabrics utilizing such yarns have been developed. Much of the development work with electrically conductive yarns has been performed with synthetic yarns wherein electrically conductive particles such as carbon particles are mixed with an extrudate to become suffused into filaments extruded from the material, thereby to render the extruded filaments electrically conductive. One of the most common forms of electrostatic dissipation fabrics incorporates such yarns at regular spacings in both the warp and weft of a woven fabric, typically a one-by-one weave. In this manner, the electrically conductive warp and weft yarns make electrical contact with one another at their various crossing points, thereby creating a regular checkerboard matrix by which electrostatic charges can be electrically conducted across the fabric. More recently, warp knitted fabrics have been developed which incorporate two sets of such conductive yarns formed in opposed lapping patterns by which the conductive yarns extend diagonally through the fabric to create a diamond-like or argyle-like pattern. In similar manner to the aforedescribed woven fabric, the electrically conductive yarns are thereby electrically connected with one another at the respective connecting points to collectively form a matrix for conducting away electrostatic charges across the fabric. These and other electrically conductive yarns and electrostatic dissipation fabrics are described and disclosed in U.S. Pat. Nos. 3,586,597; 3,806,959; 3,986,530; 4,322,232; 4,335,589; 4,606,968; 4,668,545; 4,672,825; 4,753,088; 4,856,299; 4,878,148; and 4,921,751.
It is understood that the resistivity of such fabrics to the conduction of electrical charges directly affects the effectiveness of the fabrics in dissipating static electricity. As the resistivity of an electrical conductor decreases, the ability of electricity to flow freely through the conductor commensurately increases. While the known electrostatic dissipation fabrics are generally effective for their intended purpose, the resistivity values of such fabrics are higher than would be preferred, despite the fact that known electrically conductive yarns have resistivity values within desirable ranges. Accordingly, a need exists for improvements in the construction of textile fabrics used for dissipating static electricity to obtain lower resistivity values and thereby achieve greater effectiveness in dissipating electrostatic charges.